(1) Field of the Invention:
The present invention relates to a photosensitive polymer composition and a master printing plate prepared from this composition.
In particular, the present invention relates to a photosensitive polymer composition having excellent moldability and developability, a master printing plate prepared from this composition and a printing plate having a good ink resistance. Further the present invention relates to a photosensitive master printing plate material usable for the preparation of a flexible printing plate or a flexographic printing plate having excellent moldability and water and/or alcohol developability and a good ink resistance.
(2) Description of the Prior Art:
Photosensitive polymer compositions comprising an ethylenically unsaturated compound and a photopolymerization initiator supported on a carrier polymer such as styrene/butadiene block copolymer, crystalline 1,2-polybutadiene or a polymeric elastomer such as polyurethane are known as photosensitive solid printing plate materials for flexographic printing plates (see, for example, specification U.S. Pat. Nos. 3,674,486, 4,517,278 and 3,024,180).
However, these photosensitive printing plate materials pose problems of injuring of health and environmental pollution, since these materials necessitate a halogenated hydrocarbon such as trichloroethane in the development step. Although a photosensitive polymer material for the flexographic printing plate to which the water developability is imparted has been known as described in Japanese patent publication No. 33884/1983, also this material necessitates development with alkaline water and/or an alcohol under heating. Therefore, the practical value of this material is low because a dangerous operation is required in the development. On the other hand, photosensitive solid printing plate materials for the flexographic printing plates and flexible printing plates which are to be developed with water and/or an alcohol have been proposed. These printing plate materials comprise photographic resin compositions comprising an ethylenically unsaturated compound and a photopolymerization initiator supported on an alcohol-soluble polyamide carrier or a polyesteramide carrier (see, for example, Japanese patent application Kokai publication No. 49-88606 and specification U.S. Pat. No. 4,464,456). However, the printing plates prepared from these materials are not resistant to a water ink, an alcohol ink or the like used in the flexographic printing, though they are resistant to an oil ink (i.e. an ink containing a solvent mainly comprising a hydrocarbon). Though such a photosensitive solid master printing plate has been previously solidified and it can be subjected to the exposure and subsequent processes as it is, its developability, developer selectivity, flexibilization and solvent resistance are yet unsatisfactory. In particular, no practically satisfactory solid material for the photosensitive flexographic printing plates to be developed with water or a mixture of water (main component) and an alcohol has been obtained. On the other hand, it has been known that a liquid photosensitive master printing plate material is inexpensive and has a good developability, particularly water developability, and that it can be used for the preparation of a water ink-resistant flexible printing plate (see, for example, Japanese patent application Kokai publication No. 49-109104) unlike the solid plating plate material. However, it has problems that the exposure step is complicated, that a complicated engraving machine is necessitated and that the plate thickness cannot be controlled precisely.
Now the description will be made as regards not only the flexographic printing plate materials but also general photosensitive solid printing plate materials to be developed with water or an alcohol. Photosensitive solid printing plate materials comprising a polyamide or polyesteramide soluble in water or an organic solvent, particularly an alcohol, as the carrier are known. The amount of the polyamide or polyesteramide in the photosensitive polymer composition in the photosensitive layer is 30 to 95 wt. %, practically 40 to 70 wt. %, as described in, for example, specification U.S. Pat. No. 4,481,280, Japanese patent publication Nos. 26125/1971, 32645/1975 and 28485/1982, Japanese patent application Kokai publication No. 55-79437 and specification U.S. Pat. No. 4,464,456.